The present invention relates to an information recording method for recording digital video signals or digital audio signals on optical disks and to an information recording apparatus therefor.
Optical disks are excellent in the reliability of information recording and in the preservation of recorded information, and are becoming popular as large-capacity exchangeable recording media. In recent years, because of a further increase of the recording capacity of the optical disk, the optical disk is developed to record video information, such as digital video information, and audio information, such as digital audio information, in addition to character information, such as document data and information processing programs. The capacity of an optical disk can be made larger by the increase of recording density. To increase the recording density, it is necessary to make marks (pits for example) smaller, which are means for recording information on the optical disk. When the marks are made smaller, light is liable to be scattered by small flaws on the face of the optical disk or by particles of dust, fingerprints or the like attached to the surface of the disk. As a result, information can not be recorded properly on the disk. A part of the optical disk, wherein information cannot be recorded properly owing to the flaws, dust and the like, are referred to as “defect”. It is difficult to reduce flaws on the face of the disk and dust attached to the surface of the disk. Therefore, together with the increase of the recording density, an occurrence frequency of the defects becomes higher. In recent years, various information recording methods have been proposed in order to avoid the occurrence of recording errors owing to the defects.
Information recording methods in the prior arts will be described below.
In accordance with an invention disclosed in Japanese Laid-open Patent Application Sho 63-58670, a first prior art, the recording area of an optical disk is divided into plural sectors. No information is recorded on a defective sector which is liable to cause errors owing to the defect. Information to be recorded on the defective sector is recorded on an alternate sector having been allocated previously. This recording method is referred to as an “alternate sector method.” Defective sectors are detected by scanning at high speed all of the recording areas of an optical disk in advance, and the addresses of detected defective sectors are written in a predetermined area.
In accordance with another invention disclosed in Japanese Laid-open Patent Application Hei 5-210845, a second prior art, defects of an optical disk are classified into primary defects originally present on the optical disk and secondary defects caused later owing to dust and the like attached to the disk. Respective numbers of the primary and secondary defects are then stored in respective defect lists. When the number of the secondary defects exceeds a predetermined number, disk cleaning is carried out to repair the secondary defects.
In accordance with still another invention disclosed in Japanese Laid-open Patent Application Hei 6-111479, a third prior art, when a defective sector is found, information to be recorded on the defective sector is recorded on a first normal sector adjacent to the defective sector. Information to be recorded on the first normal sector is recorded on a second normal sector adjacent to the first normal sector. In this way, information is recorded on adjacent normal sectors one after another. As a result, information is recorded only in normal sectors one after another by avoiding recording in the defective sectors. This method is referred to as a “slipping method.”
Each of the prior art described above is applicable to discontinuous information having relatively small information units such as computer data, not causing problems even when the information are recorded on plural sectors spaced apart from each other on an optical disk. The above-mentioned video or audio information has a large amount of information per unit time. Furthermore, a continuous long recording time is required, and the whole amount of the information is extremely large. For example, since video information includes a large amount of continuous information, a recording unit of information is required to be larger. In a CD-ROM for example, one error correction block corresponding to the recording unit has 2 KB of recording capacity. On the other hand, in a DVD (digital versatile disk) mainly used for recording video information, one error correction block has 32 KB of recording capacity. When the alternate sector method or the slipping method in the above-mentioned prior arts is applied to the DVD, and one defect is present in one error correction block of 32 KB corresponding to one sector, an area having a recording capacity of 32 KB is removed from use. Defects are caused by flaws on the face of the disk in most cases. Even when a small spot-like flaw having a diameter of about 1 mm is present on the face of the disk for example, the flaw affects about 1000 tracks. For this reason, if the above-mentioned alternate sector method is applied to units of one error correction block of 32 KB, an area having a recording capacity as many as 32 MB (32 KB×1000) becomes unusable. Furthermore, the defect appears once at every turn of the disk periodically on about 1000 tracks. In the DVD, the recording capacity of the error correction block of 32 KB is approximately equal to the recording capacity of one innermost track. In the case that the above-mentioned flaw is present near the innermost track, data processing based on the alternate sector method or the slipping method must be carried out incessantly in recording operation to inner 1000 tracks. This data processing causes very large data processing operation, and results in serious trouble in sequential recording of the video information supplied continuously. In the worst case, recording operation is liable to be interrupted.